Specifying data for a point in time before the actual printing process takes place per se precludes the further transmitting of information concerning the success or the quality of the printing process. For example, if a barcode is inserted to communicate the order number to the further processing location, this barcode is inserted into the image either during the imposition or during the raster image process. The barcode is then transferred to the paper during the printing process. In the event that interference occurs during the printing process, for example as a result of a stop command, the barcode can no longer be changed. The further processing equipment will read in the bar code, but it cannot determine whether the printing quality of the respective printed sheet is good.
The following examples are provided for the illustration:
Data is transmitted via a barcode that is affixed to the center of the printed sheet. The printing press is stopped abruptly because of an internal error. One of the two following situations then occurs on a random basis which is based on the point in time for the stop:
The stop is before the barcode or during the reading of the barcode. The further processing equipment cannot read in the barcode. The respective printed sheet cannot be detected and/or allocated and is discharged. The end product is consequently removed even though it is free of defects.
The stop position is after the barcode. The further processing equipment can read in the barcode. The respective printed sheet is detected and/or allocated correctly. The printed sheet ends up as good-quality sheet in the end product with the result that the end product is no longer free of defects.
The printing on of specific marks which are again read in by the further processing equipment is also widely used. The control unit for a cross-cutter, for example, traditionally operates with the aid of cutting marks while a book separation occurs with the aid of separating marks. The simplicity of this solution is advantageous since only positions and, if applicable, also release zones need to be defined. (Concerning the codified print marks, please see the EP2481585 A1.) The extremely restricted function options are a disadvantage (binary information: mark is there or is not there).
Also widely used is the method of printing on barcodes, or point codes, or similar detection characteristics which can be read via suitable sensor devices into the further processing equipment. More or less extensive amounts of data can thus be transmitted further. This method is frequently used for the product identification, for example for the purpose of order data allocation or for personalized products. The advantage is again the relatively easy application. The necessity of affixing additional marks, however, is a disadvantage since the position of a barcode in most cases cannot be used for precise adjustments (e.g. for the cross cutter).
Also known are applications where the printing system transmits information via data communication to the further processing equipment. For example, this is achieved in concrete terms with the aid of a UP31 protocol. This solution has the advantage of a nearly unlimited amount of data which can thus be transmitted further, but also has the disadvantage that it is difficult to allocate the datagrams to a physical paper position. In most case, this takes place via theoretically conveyed paper lengths, but frequently requires additional barcodes or marks.
In summary, we can state that all the aforementioned methods can be used to transmit more or less data from the printing system to the further processing equipment. The data for the most part relate to the product flow (signature number, order characterization) or serve as a trigger for the operational control (cross cutter; deflector systems, selective feeding). All printed-on information is chronologically fixed to the point in time before the printing. The known datagram solutions replace or supplement in the same way the printed-on information.
Information is furthermore accumulated in the printing system which cannot be transmitted via barcodes transmitted in advance, e.g. the marking of the last printed sheet of an order. The imposition of the printed sheet always relates to a copy of the product which is then printed repetitively in an optional number. Thus, the last copy of an order cannot contain a different barcode. This could only be realized with a barcode affixed in real time, within the context of the raster process, which is tied to high expenditure and would result in posing high requirements for the data management of the printing system.